1. Field of Invention
The invention relates to a fluid supply systems, to a solid-phase adsorbent material useful for storing and dispensing fluids of low vapor pressure, and to a solid-phase sorbent material useful for storing and dispensing liquefied fluids.
2. Description of the Related Art
In a wide variety of industrial processes and applications, there is a need for a reliable source of process fluids. Such process and application areas include, but are not limited to, semiconductor manufacturing, ion implantation, manufacture of flat panel displays, medical intervention and therapy, water treatment, emergency breathing equipment, welding operations, space-based delivery of liquids and gases, etc.
Conventionally, processing fluids are supplied for commercial applications by means of high-pressure cylinders containing compressed processing fluids. However, such conventional high-pressure gas cylinders are susceptible to leakage from damaged or malfunctioning regulator assemblies, as well as to rupture if internal decomposition of the gas leads to rapid increase of interior gas pressure in the cylinder. These deficiencies pose a risk of unwanted bulk release of gas from the cylinder. Such bulk release in turn can create very hazardous and even catastrophic conditions where toxic or otherwise hazardous fluids are involved, particularly during transportation and shipment of fluid cylinders when back-up scrubbing or other safety systems may not be present.
To overcome these inherent problems of high-pressure gas cylinders, sorbent-based fluid storage and dispensing systems may be employed, of the type disclosed in U.S. Pat. No. 5,518,528, issued May 21, 1996 in the names of Glenn M. Tom and James V. McManus. Such sorbent-based fluid storage and dispensing systems effectively reduce the interior gas pressure by reversibly adsorbing sorbate fluid onto a physical sorbent medium disposed inside a containment vessel.
Sorbent-based fluid storage and dispensing systems of such type significantly reduce the risk of gas leakage and cylinder rupture associated with conventional high-pressure gas cylinders. These systems typically utilize physical sorbent materials, such as silica, carbon molecular sieves, alumina, polymers, kieselguhr, carbon, and aluminosilicates, having average pore sizes in a range of from 4 Angstroms to 13 Angstroms. Although these sorbent materials of such pore size character are effective for reducing pressure of certain high vapor pressure fluids (e.g., AsH3, PH3, and BF3), they are not satisfactory for purpose of storing and delivering fluids of low vapor pressures (i.e.  less than 200 psig at room temperature), especially the reactive fluids, for the following reasons.
First, such sorbent materials are chemically incompatible with low vapor pressure gases such as ClF3, WF6 and Br2, reacting with the gases to form unwanted byproducts.
Further, such conventionally employed sorbent materials, due to their respective pore size distributions, are oftentimes characterized by adsorption potentials that are too high. They cannot effectively desorb low vapor pressure gases from the sorbent, and therefore are inadequate to deliver low vapor pressure gases to the tool under normal application conditions. The term xe2x80x9cnormal application conditionsxe2x80x9d is hereby defined as fluid delivery conditions characterized by a decrease of pressure from 650 torr to 10 torr at room temperature.
For example, sorbent materials of the type disclosed by the Tom et al. patent, which are characterized by (1) average pore sizes in the range of 4-13 Angstroms and (2) porosity in the range of 30-40%, measured as [gross volume of sorbate/gross volume of sorbent material including voids]xc3x97100%, are only able to desorb 10-20% of the low vapor pressure gases such as Br2 under normal application conditions, while the same sorbent materials can desorb 70-90% of the high vapor pressure gases such as arsine (AsH3) and phosphine (PH3). U.S. Pat. No. 6,089,027, issued Jul. 18, 2000 in the names of Luping Wang and Glenn M. Tom, describes an improved gas storage and dispensing system for storage and dispensing of low vapor pressure liquefied gases such as ClF3, WF6, GeF4, and Br2, etc., in which a fluid pressure regulator is disposed inside of the fluid storage and dispensing vessel. The fluid pressure regulator functions as a flow control device, which can be set at a predetermined pressure level, to dispense fluids from the vessel at such pressure level. Such xe2x80x9cregulator in a bottlexe2x80x9d arrangement provides an effective system for storage and dispensing of liquids and gases at pressure levels that vary from about 50 psig to about 5000 psig, depending on the specific end use application. When the pressure is set at a subatmospheric level, it can effectively eliminate the hazards of gas leaking out of the vessel in case of development of an external leak during cylinder transportation. The xe2x80x9cregulator in a bottlexe2x80x9d arrangement is also ideal for safe storage and delivery of very low vapor pressure (less than 14.7 psia) pyrophoric organometalllic fluids such as trimethyl aluminum, dimethyl aluminum hydride, etc. When storing pyrophoric fluids of very low vapor pressure, the xe2x80x9cregulator in a bottlexe2x80x9d arrangement with the subatmospherical setting can effectively prevent air from leaking into the cylinder if an external leak develops during cylinder transportation and handling, therefore eliminating the potential fire and other hazards caused by reaction between the pyrophoric fluids and the air.
However, when the fluid storage and dispensing vessel of Wang et al. patent is used for liquefied gases, the fluid pressure regulator is susceptible to malfunction, because liquefied gases can easily enter the regulator and cause discharge pressure instability. In applications such as semiconductor manufacture, the maintenance of precisely controlled flow characteristics (temperature, pressure, flow rate and composition) is critical to the achievement of satisfactory product microelectronic device structures. In such applications, the pressure instability incident to liquid ingress to the regulator compartment causes the occurrence of process perturbations that may render the product microelectronic device structure unsatisfactory or even wholly useless for its intended purpose.
Moreover, during the fluid delivery process significant cooling occurs when the liquefied gas is evaporated from the storage cylinder, due to the heat loss of vaporization. The cooling will significantly reduce the vapor pressure of the liquefied gas, resulting in insufficient evaporation and slowing down gas flow from the cylinder. One or more heat-exchange units are usually provided on the external wall of the cylinder, for externally supplying thermal energy to the liquefied gas to compensate for the heat loss caused by evaporation. However, the conventional sorbent materials have low thermal conductivities and are therefore ineffective for transfering heat to the liquefied gas inside the cylinder. Insufficient heat transfer causes uneven distribution of thermal energy in different portions of the cylinder, i.e., overheating of the exterior of the cylinder and underheating of the interior of the cylinder.
The art has not found a solution to the above-described problems associated with low vapor pressure fluids or liquefied gases, with respect to sorbent materials having good sorptive affinity, good capacity loading characteristics, good chemical stability, good desorption characteristics, good thermal conductivity, or of liquid containment and occlusion from the regulator element in internal regulator-based fluid storage and dispensing systems.
There is accordingly a need in the art for a physical sorbent material that is chemically compatible with low vapor pressure fluids, that has an adequate pore size, porosity and pore size distribution to reduce storage pressure of low vapor pressure gases via reversible adsorption of such gases, and that enables the sorbate fluid to be readily desorbed from the physical adsorbent material for discharge from the vessel during dispensing operation.
There is concurrently a need in the art for a solution for the liquid ingress problems associated with the use of internal regulator-based fluid storage and dispensing systems.
The present invention resolves the aforementioned problems by the use of a solid-phase sorbent medium for storing and dispensing a low vapor pressure fluid, in which such solid-phase sorbent medium can effectively desorb the low vapor pressure fluid therefrom under normal application conditions. Further, the present invention is useful for storing and dispensing a liquefied gas, in which such solid-phase sorbent medium functions as a protective medium to prevent the liquefied gas from entering into the regulator element in an internal regulator-based fluid storage and dispensing system.
The solid-phase sorbent medium of the present invention is a porous metal matrix comprising at least one, Group VIII or IB metal or metal alloy.
The porous metal matrix may comprise any Group VIII or IB metal or metal alloy that is chemically compatible with the low vapor pressure fluid, accommodating the sorption and desorption of the fluid without adverse reaction or other interaction. The porous metal matrix thus may comprise metals selected from the group consisting of iron, nickel, cobalt, ruthenium, rhodium, palladium, osmium, iridium, platinum, copper, silver, gold and alloys, blends and combinations of one or more of the foregoing metal species.
The term xe2x80x9clow vapor pressurexe2x80x9d, when used herein, means vapor pressure of less than 200 psig, measured at room temperature. Low vapor pressure fluids of particular interest in the general practice of the invention include, but are not limited to, ClF3, WF6, HF, GeF4, Br2, and the like.
Among Group VIII metals, nickel and iron have been discovered to be particularly compatible with low vapor pressure fluids and therefore are highly advantageous materials for forming the porous metal matrix. In a particularly preferred embodiment of the present invention, stainless steel is used as a material of construction for the porous metal matrix.
In one aspect of the invention, the porous metal matrix constitutes a solid-phase metal adsorbent medium for adsorbing low vapor pressure liquids, having (1) an average pore diameter in the range of from about 0.5 nm to about 2.0 nm and (2) a porosity in the range of from about 10% to about 30%. The pore size distribution of such solid-phase metal adsorbent medium is preferably characterized by about 80% to about 90% of pores having a diameter in the range of from about 1.5 nm to about 2.0 nm, and about 10% to about 20% of pores having a diameter greater than 2.0 nm.
The solid-phase metal adsorbent medium of the invention, as described hereinabove, is capable of reducing the pressure of low vapor pressure fluids to subatmospheric pressure levels on the order of 12.6 psia/0.85 atm.
Such solid-phase metal adsorbent medium may also contain non-metal adsorbent particles that are dispersed in a porous Group VIII or Group IB metal matrix, or alternatively, such solid-phase metal adsorbent medium may comprise non-metal adsorbent particles that are coated with Group VIII or IB metal(s) or metal alloy(s). Useful non-metal adsorbent particles in practice of the present invention include, but are not limited to, zeolites, carbon materials, porous silicon. polymers, aluminum phosphosilicate, clays, and combinations of two or more thereof. Among these non-metal adsorbent materials, zeolites and carbon materials, or combinations thereof, are preferred. Preferably, the average pore size of the non-metal adsorbent particles is less than 500 xcexcm and more preferably in a range of from about 0.5 nm to about 50.0 nm.
In another aspect of the invention, the porous metal matrix constitutes a solid-phase metal sorbent medium for containing and immobilizing liquefied gases in an internal regulator-based fluid storage and dispensing system, having (1) an average pore diameter in a range of from about 0.25 xcexcm to about 500 xcexcm and (2) a porosity in a range of from about 15% to about 95%. The solid-phase metal sorbent medium in this embodiment is particularly effective for immobilizing the liquefied gases and preventing such gases from entering into the fluid pressure regulator and iterfering with its proper operation.
Yet another aspect of the present invention relates to a process of forming the porous metal matrix, comprising the steps of:
providing fine metal particles of at least one of Group VIII metals, Group IB metals, and alloys thereof, and
sintering such fine metal particles, e.g., in a sintering furnace, to form the porous metal matrix.
The term xe2x80x9cfine metal particlesxe2x80x9d as used herein means metal particles having an average particle size of not more than about 1000 xcexcm and preferably not more than about 500 xcexcm. More preferably, the fine metal particles used in the practice of the present invention have an average particle size in the range from about 20 nm to about 1 xcexcm.
Sintering of the fine metal particles may be carried out in a sintering furnace or in other suitable manner, at an appropriate temperature, e.g., a temperature in a range of from about 20xc2x0 C. to about 1500xc2x0 C., to ensure formation of a continuous metal matrix without destroying the porosity of the fine metal particles being sintered.
In a still further aspect of the present invention, the porous metal matrix is formed by a process comprising the steps of:
forming a solid-phase matrix comprising at least one Group VIII or IB metal and an oxidizable carbon-containing material; and
heating such solid-phase matrix in the presence of an oxidizing agent to gasify the oxidizable carbon-containing material.
Oxidizable carbon-containing materials useful in the practice of the present invention include, but are not limited to, elemental carbon materials, such as graphite, diamond, amorphous carbon, etc., as well as various hydrocarbon compounds. Preferably, the oxidizable carbon-containing materials comprise hydrocarbon compounds. However, such preference is not intended to limit the broad practice of the present invention. One ordinarily skilled in the art can readily determine, without undue experimentation, other suitable species of carbon-containing materials for the purpose of practicing the present invention, according to specific operational requirements and conditions.
The oxidizing agent useful in the practice of the present invention may include any suitable oxidizer commonly used and well-known in the art. In one preferred embodiment, such oxidizing agent is selected from the group consisting of elemental oxygen, oxygen gas (O2), ozone, air, and combinations thereof. Other kinds of oxidizers can also or alternatively be employed, as will be readily determinable by one ordinarily skilled in the art.
In another specific aspect of the present invention, the porous metal matrix is formed by a process including the following steps:
forming a solid-phase matrix comprising at least one Group VIII or IB metal and soluble metal oxide particles; and
immersing such solid-phase matrix in an acidic solution to dissolve said soluble metal oxide particles.
The term xe2x80x9csoluble metal oxidexe2x80x9d, as used herein, means a metal oxide dissolvable in an acidic solution.
Preferably, the soluble metal oxide particles comprise at least one metal component selected from the group consisting of Fe, Ni, Ag, and Pt. The soluble metal oxide particles can be of any suitable particle size and particle size distribution characteristics.
Another aspect of the present invention relates to an adsorption-desorption apparatus, for storage and dispensing of a low vapor pressure fluid, comprising:
a storage and dispensing vessel constructed and arranged for holding a solid-phase metal adsorbent medium;
a solid-phase metal adsorbent medium disposed in said storage and dispensing vessel at an interior gas pressure, said solid-phase metal adsorbent medium comprising a porous metal matrix including at least one Group VIII or IB metal;
a low vapor pressure fluid adsorbed on said solid-phase metal adsorbent medium; and
a dispensing assembly coupled in gas flow communication with the storage and dispensing vessel, and arranged for dispensing from the vessel the low vapor pressure fluid desorbed from the solid-phase metal adsorbent medium.
A further aspect of the invention relates to a fluid storage and dispensing system, comprising a vessel holding a solid-phase metal adsorbent medium having a low vapor pressure fluid adsorbed thereon, such vessel including a port having dispensing means associated therewith for controllably dispensing the low vapor pressure fluid desorbed from the solid-phase metal adsorbent medium in a dispensing mode of operation of the system, wherein the solid-phase metal adsorbent medium includes a porous metal matrix comprising at least one Group VIII or IB metal.
Such solid-phase metal adsorbent medium preferably has (1) an average pore diameter in a range of from about 0.5 nm to about 2 nm, and (2) a porosity in a range of from about 10% to about 30%.
Exclusive of the solid-phase metal adsorbent medium of the present invention, such adsorption-desorption apparatus may be of a general type described in U.S. Pat. No. 5,518,528 for xe2x80x9cStorage and delivery system for gaseous hydride, halide, and organometallic group V compounds,xe2x80x9d issued May 21, 1996 to Glenn M. Tom and James V. McManus, the disclosure of which is incorporated by reference herein in its entirety.
Yet another aspect of the present invention relates to a fluid storage and dispensing apparatus, for storage and dispensing of a low vapor pressure liquefied gas, comprising:
a storage and dispensing vessel constructed and arranged for holding a solid-phase metal sorbent medium;
a solid-phase metal sorbent medium disposed in said storage and dispensing vessel at an interior gas pressure, said solid-phase metal sorbent medium comprising a porous metal matrix including at least one Group VIII or IB metal;
a low vapor pressure liquefied gas sorbed by said solid-phase metal sorbent medium;
a fluid dispensing assembly coupled in gas flow communication with the storage and dispensing vessel, and arranged for dispensing from the vessel gas derived from the low vapor pressure liquefied gas; and
a fluid pressure regulator associated with the fluid dispensing assembly, and arranged to maintain a predetermined pressure in the interior volume of the vessel,
wherein the fluid dispensing assembly is selectively actuatable to flow gas, derived from the low vapor pressure liquefied gas sorbed by said solid-phase metal sorbent medium, through the fluid pressure regulator, for discharge of the gas from the vessel.
Preferably, such metal sorbent medium for sorbing the low vapor pressure liquefied gas is characterazed by (1) an average pore diameter in a range of from about 0.25 xcexcm to about 500 xcexcm and (2) a porosity in a range of from about 15% to about 95%.
More preferably, the fluid storage and dispensing apparatus of the present invention further comprises one or more heating elements for supplying thermal energy to compensate for heat loss during the evaporation of the low vapor pressure liquefied gas. Such heating elements may be constructed and arranged in any manner to supply thermal energy to the low vapor pressure liquiefied gas. For example, such heating elements may be dispersed among the sorbent medium inside the storage and dispensing vessel; alternatively, such heating elements may be disposed on an external wall of the storage and dispensing vessel and supply thermal energy to the liquefied gas through thermal conduction. The solid-phase metal sorbent medium preferably has high thermal conductivity for effectively conducting the thermal energy from the external wall of the storage and dispensing vessel to the liquefied gas stored therein.
Exclusive of the solid-phase metal sorbent medium of the present invention, such fluid storage and dispensing apparatus may be of a general type described in U.S. Pat. No. 6,089,027 for xe2x80x9cFluid storage and dispensing system,xe2x80x9d issued Jul. 18, 2000 to Luping Wang and Glenn M. Tom, the disclosure of which is incorporated by reference herein.
Yet another aspect of the present invention relates to a process for supplying a low vapor pressure fluid reagent, comprising:
providing a storage and dispensing vessel containing a solid-phase metal adsorbent medium having a sorptive affinity for said low vapor pressure fluid reagent;
sorptively adsorbing the low vapor pressure fluid reagent on the solid-phase metal adsorbent medium at an interior gas pressure to yield a sorbate fluid-retaining metal adsorbent medium;
desorbing sorbate fluid from the sorbate fluid-retaining metal adsorbent medium; and
dispensing the desorbed fluid from said storage and dispensing vessel;
wherein the solid-phase metal adsorbent medium comprises a porous metal matrix including at least one Group VIII or IB metal.
In a still further aspect, the invention relates to a method of supplying a low vapor pressure fluid to a process requiring same, such method comprising sorptively retaining the low vapor pressure fluid on a solid-phase adsorbent including a porous metal matrix comprising at least one Group VIII or IB metal, and desorptively removing the low vapor pressure fluid from the adsorbent and transporting same to the process when the process requires same.
Yet another aspect of the invention relates to a method of suppressing pressure perturbations of a fluid storage and dispensing system including a storage and dispensing vessel for holding a low vapor pressure liquefied gas therein, a discharge assembly disposed on the vessel for dispensing the low vapor pressure liquefied gas therefrom, and a gas flow regulator inside the vessel arranged for flow therethrough of gas deriving from the low vapor pressure liquefied gas, so that gas flows through the regulator prior to flow through the discharge assembly, wherein the pressure perturbations are occasioned by ingress of the low vapor pressure liquefied gas into the regulator, such method comprising shielding the regulator from contact with the low vapor pressure liquefied gas with a body of solid-phase metal sorbent medium arranged in the vessel to sorptively immobilize any low vapor pressure liquefied gas that would otherwise flow into the regulator, such metal sorbent medium including a porous metal matrix comprising at least one Group VIII or IB metal. Preferably, such metal sorbent medium is characterazed by (1) an average pore diameter in a range of from about 0.25 xcexcm to about 500 xcexcm and (2) a porosity in a range of from about 15% to about 95%.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.